The invention concerns cold rolling mills for the production of ferrous and non-ferrous seamless tubes.
Various processes are employed for making seamless tubes of mild or medium steel.
The best known of these is one that basically uses a perforating mill and a "pilgrim" or "pilgrim process" mill.
In this rolling mill there are two parallel eccentrically contoured rollers turning in opposite directions.
When the rollers open the perforated preformed forging is presented in the direction opposite to that which determines movement of the material during the rolling process.
A cylindrical steel mandrel, of a diameter the same as that of the tube required, is inserted in the hole.
A preformed forging already mounted in position is pressed forward through the opening in the rollers by an hydraulic assembly.
Simultaneously, at each turn of the rollers, forward movements of the forging, introduction of material to be forged by the surfaces of the rollers supported by the cells for loading and stretching the metal, are repeated.
At the end of each stage in the process a fresh length of tube is brought forward by the feed assembly and rolled.
A feed mechanism makes it perform a short backward movement so that a new portion of tube is rolled in the subsequent sequence.
Smoothing and processing racks complete the installation.
It frequently happens that the great forces involved and the high stresses to which the metal is subjected cause breakages in the preformed forging, according to the type of material concerned, when such stresses exceed certain levels.